The use of relays is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems for providing protection against over-current conditions and earth-fault protection. In power system protection, static auxiliary powered relays for over-current and earth-fault protection are used. In such designs, the source of energy used by an electronics circuit is independent of current sensors. The current sensors in this situation encounter very low and constant burden and small linearity range, for example 20 times the nominal design current, which facilitates freeing the secondary current waveform of any significant distortion. The current sensors are therefore light in weight and smaller in size. Also the current sensors follow primary high current sensors.
For measurement of the current through the current sensors, the control electronics derives the operating power from an auxiliary power supply, which facilitates realization of an active filter design including signal conditioning. The auxiliary power supply supplements use of a dual polarity voltage supply, enabling implementation of simple and active filter conditioning. The high power demand of an electronics circuit can be supplied easily. In other words, a design flexibility in terms of components selection and features to be embedded is available.
There are however certain situations, where an installation can encounter constraints for supporting an auxiliary power supply for the relay operation (e.g., for Ring Main Units installation in urban cities), and a self powered relay per se. However, in the case of self powered relays per se, the energy used by the relay electronics circuit is to be supplied with at least one measuring current sensor. This implies that the current sensors provide measurement of current including the power supply. Based on a power consumption of the control electronics, the current sensors VA capacity can be influenced. Further, the approach for power extraction from the current sensor can introduce distortion in the basic current sensor waveform due to dynamic impedance faced by the sensor owing to the specifications for restricting power dissipation over the operating current range. Such a specification can call for current sensors with greater VA capacity and greater linearity range. The current sensors can therefore be bulky. To address relay performance in this situation with at least possible current sensor size and VA, optimal balance of the control electronics design hardware and the associated software is desired.
U.S. Pat. No. 7,304,828 discloses an AC/DC intelligent solid state relay/breaker device with current/temperature sensing, time-delay overloads and over-current/over-temperature protection. In this disclosure, power MOSFETs or other transistors, control a load current. A bypass current sensing path monitors the MOSFET current and causes a shutdown through signal processing in the event of an over-current condition. Phase and earth fault protection are not disclosed because the device is used as a series element in a power flow configuration.
U.S. Patent Publication No. 20060007627 discloses an intelligent MOSFET based relay system that responds to a variety of influences. The relay system includes at least one relay, at least one peripheral sensor collecting data related to the relay system, and a control logic section linked to the relay and the sensor. The control logic section is further linked to a control computer via a communication interface. The control logic section intelligently controls operation of the relay based upon instructions received from the control computer and data collected via the at least one peripheral sensor and the relay. The system is adapted for use in a networked arrangement. The control computer is disclosed as passing instructions for controlling operation of relay.
Patent No. WO/2007/114951 is related to the field of industrial control systems, protection and control mechanisms and/or methodologies for electrical motors and other electrical devices. This document discloses protection and control of electrical devices, and can provide for wide-range current measurement, self-calibration, and wide-range line-powered electronics to provide application flexibility and reliability, and cost-effectiveness. An overload relay can be employed along with an electromagnetic contactor, consistent with the application, as a component in industrial control systems. This patent describes use of an auxiliary supply with applications for electrical motors.
U.S. Pat. No. 7,016,174 describes a system for an electronic trip unit whereby reliable instantaneous protection is provided. A multi-algorithmic approach uses an algorithm to detect bolted faults based on a direct comparison of the current and a threshold value, and an additional algorithm to detect current overloads based on a comparison of a peak-to-peak current and an additional current threshold. User configurability is not discussed in this patent.
In U.S. Pat. No. 7,248,451, a power controller is positioned within a current path between a line side and a load side of an electrical circuit. The power controller closes the current path in the presence of a control supply and opens the current path in the absence of the control supply. A power supply electrically connected to the current path provides the control supply. A sensor system receives power from the power supply, monitors current in the current path and outputs a sensor signal indicative of a current condition within the current path. A logic controller also receives power from the power supply, receives the sensor signal and removes the control supply from the power controller when the sensor signal does not satisfy established criteria. The sensor system may include either or both of: imbalance sensors for monitoring the current balance among two or more electrical lines; and over-current sensors for monitoring current in individual lines. The control of the supply-auxiliary power source indicates that the current relays used in the sensor system do not constitute a self-powered relay per se.
U.S. Patent Publication No. 20060050464 relates to a control system, such as a control system having a solid state relay in a hockey puck configuration for controlling power to a power-receiving load. A first bus bar and a second bus bar are configured to include a current sensing portion. A communication interface is adapted for compatibility with communications involving a WatBus™, Dallas Semiconductor one-wire protocol, a Seriplex, a sensor bus, a DeviceNet™, bus, a FMS, Lon Works, a Control Area Network (CAN), an Interbus S, an SDLC, AS-Interface (AS-i), a Local Interconnect bus (LIN-bus), an IEEE-1118 bus, a Profibus, Modbus RTU, an enterprise communication bus including an Ethernet TCP/IP, an Internet, a token ring LAN, an Ethernet LAN, an FDDI network, a private data network, an ISDN, and a VPN. This patent discusses a solid state relay with a variety of custom communication capacity.
U.S. Pat. No. 7,031,131 relates to an over-current protection device for detecting a current flowing through a conductor and for shutting off the current when the current exceeds a predetermined threshold value. A current sensor which constitutes an overload protection apparatus and senses a current supplied from a power source to a load is constituted by providing a magnetic sensor having the effect of magnetic impedance (MI), an AC supply which impresses AC on this sensor, a bias current supply means which supplies a bias current to a bias coil, a peak sensor which senses the peak or a change in impedance of the magnetic sensor as a change in voltage, and a switch which selects the output of the peak sensor in accordance with each phase. A holding device which holds switch outputs one after another and an amplification device are provided in common to enable current sensing for each phase. Thus, a range of current sensing is enlarged to reduce power consumption and cost. This patent discloses using an AC supply to impress the sensor, and using bias current supply for biasing bias coil.
U.S. Pat. No. 6,888,712 relates to a single protection device, including a transformer, an input circuit, and a switch circuit, suitable for addition to an electrical power system that includes a control panel electrically interconnected with a starter to control an electrical device. The patent discloses a starter with varied functional blocks.
U.S. Pat. No. 6,421,216 discloses an overcurrent protection system giving rapid response to relatively small overcurrents. It has a sensor element and an interruption element in series between a power source and a load. The sensor element is functionally linked to the circuit interruption element via a control element. When current exceeds a predetermined amount, the sensor element transfers heat to the control element, which causes the circuit interruption element to change from a conducting state to a non-conducting fault state. The control element may include a PTC device. This patent discloses thermal considerations-heat transfer for operations, versus electrical sensing of current magnitudes through interfacing current transformers.
U.S. Pat. No. 6,055,145A describes a microprocessor based overcurrent trip unit which generates trip signals as an adjustable function of current and time, and has a visual representation of the trip function on a front panel with 2-color LEDs associated with the trip function serving as indicators of trip conditions when red, and of a selected programmable parameter when green. The green LEDs flash to indicate a parameter selected for modification in a program mode and illuminate steady in a view mode.
U.S. Pat. No. 6,459,557 discloses a configurable overload relay selectively operable in a single-phase mode of operation and a multi-phase mode of operation configured to sense current flow through power conductors. The relay is further configured to determine a parameter related to the current flow, such as average current, vector sum of phase currents, and current imbalance, based on selection of either the single-phase or multi-phase mode of operation. Regardless of the selected mode of operation, the relay can provide protection for multiple types of power conductor fault conditions, including ground faults, overloads, and phase loss. The relay further can be configured to provide a reporting signal indicative of the value of the determined current-related parameter and/or the occurrence of the fault condition. Thus, the patent discloses two distinct modes of operation.
Patent No. RU2179775 discloses a reference-voltage source and 2 (two) AND gates whose outputs are connected to an input of a final element; a first input is connected to an output of an OR gate, and a second input is connected to an output of a signal shaper that functions to record critical overcurrent; other outputs of the signal shaper are connected to respective inputs of a time-setting circuit and the current sensor is inserted in series with a circuit under protection. First inputs of the signal shaper are connected to its output through a voltage divider and second inputs are connected to respective levels of reference voltages. In this way, the device provides for protecting DC and AC power circuits and realizes single-valued current and time settings due to a discrete principle of control. The patent discloses protecting DC and AC power circuits with gated logic without mention of an operating source of power.
U.S. Pat. No. 4,077,055 provides a self-powered self-contained ground fault protective device including a current monitor, an electronic circuit for amplifying the output of the current monitor, a relay connected to the amplifying circuit and adapted to operate whenever the ground fault current, through the current monitor, rises above a predetermined level, and an interchangeable rating plug for activating a circuit board switch. The current monitor, amplifying circuit, and relay are all supported and enclosed by a molded insulating housing. The rating plug is inserted into a socket on the exterior of the housing. This patent appears to be more of a mechanical plug in construction for ground fault instead of truly a self powered relay suited for phase faults.
Patent No. EP 0469207 discloses a self powered multiple phase circuit protection device including a plurality of current transformers connected in parallel with each other and adapted to be individually associated with one phase of a multiple phase load and for providing signals representing the current flowing in an associated phase. A switch is adapted to be actuated to interrupt power to the multiple phase loads, and a fault determining circuit is connected to the circuit transformers and to the switch for actuating the switch for at least one predetermined condition of the current signals. Functionality is average current based.
The disclosures of all of the foregoing documents are incorporated herein by reference in their entireties.